Skin penetration is a common procedure in various biomedical applications, particularly in minimally invasive drug delivery (via microneedles) where instant detection and/or great precision of skin penetration is desired. The ability to penetrate the skin reproducibly to a precise depth enables drugs to be delivered to the desired layers, which is currently the state of the art in transdermal drug delivery (i.e. delivering drug across and into the skin).
Other applications requiring precise control of skin penetration is body interstitial fluid extraction, e.g. blood sampling for blood content analysis. Blood sampling involves pricking a body site such as the finger tip or forearm to obtain a small amount of blood. The amount of blood is directly related to the wound created by a lancet. Since blood testing technology requires less and less blood for accurate testing, there exists a need to precisely control the penetration depth as it is also directly related to the trauma incurred. The deeper the penetration, the more traumatic and painful it is.
Lancets are small pointed needles used in pricking the body site to obtain small amount of blood for testing or blood sampling in general. Stainless steel lancets are currently used due to its strength and ease of maintenance. For a typical manufacturing process, a stainless steel wire needs to be cut into correct length and then ground to the desired sharpness. The cut and ground wire is then inserted into a mold set for injection molding a plastic component for safety containment and handling. There are several inherent problems associated with the prior art.
Stainless steel lancets are stiff and hard, and this is a potential risk of injury during the handling or disposal of these lancets. As the lancets are to be destroyed after use, there is a risk of infection. Stainless steel has very high melting temperature (1,420° C.), making the incineration process of used lancets very inconvenient for hospitals. There is a need to have lancets that can be functionally disabled after use. There is also an urgent solution required for the incineration or recycling of these bio-hazardous disposables.
Currently, the blood sampling process involves pricking a body site with a stainless steel lancet and collecting the blood sample using a test media such as a plastic test strip. It would be advantageous if the lancet, apart from pricking a body site, can also be used to collect or store the blood sample and/or then transport it to a location accessible for testing means. However, stainless steel having high strength and stiffness is not as suitable a candidate as polymers for incorporating these features on the lancet.
As an alternative, lancets are also made of plastic. However, these plastic lancets merely consist of solid tip for pricking or a channel for transporting the blood. There are still unsolved problems associated with these plastic lancets. Most plastic lancets with transport channel remains in the body for body fluid extraction. This procedure also contributes to an increased traumatic experience.
Most existing lancets are unable to perform sensing functions, such as detecting skin penetration or sensing the depth of penetration. The ability to control the depth of penetration allows pain to be managed effectively, and it also allows confirmation that a desired depth for drug delivery is achieved.
On the other hand, there have been several recent proposals to provide for measurements of penetration depth in lancets. However, in most of the proposed techniques, the depth of penetration is derived from the measurement of the absolute electrical characteristics of the skin, which involves correlation of measurements and calibration of equipment. This is imprecise and impractical for transdermal drug delivery.
The electrical properties of skin, change according to environmental and physiological factors and differ greatly from person to person and bodily regions. Most of the abovementioned proposals merely measure the absolute values of these properties directly, requiring too many precedent correlations before use, which can be impractical. For example, those described by US 2002/0042594 entitled “Apparatus and method for penetration with shaft having a sensor for sensing penetration depth” and US 2002/0010414 entitled “Tissue electroperforation for enhanced drug delivery and diagnostic sampling” do not address the wide variance of the impedance of the skin due to physiological and environmental factors. Although WO 2004/080306 entitled “System and method for piercing dermal tissue” attempts to address this issue, by averaging absolute values measured with multiple reference electrodes so as to alleviate the variance in skin impedance due to humidity, it fails in that it is dependent on many correlations having to be performed prior to actual use.
A need therefore exists to provide a system and method for detecting and measuring the depth of skin penetration that seeks to address at least one of the abovementioned problems.